1. Field of the Invention
The field of art to which this invention pertains is that of pneumatic tires and more particularly to the tread portion of all-season pneumatic tires. It should be noted that the tread of the present invention can be used on all types of tire constructions, all sizes of tires as well as retreading and centrifugally cast tires.
2. Description of the Prior Art
A current trend in tire design is in the area of "all season" tires wherein the tread design must have good traction in all weather conditions, without compromising snow or wet traction. It should be understood that the design of a specific tread design involves trade-offs between specific tire performance characteristics in order to achieve the overall desired tire performance. For example, a tread design which is basically comprised of lateral bars has the following characteristics: (1) deficient lateral stability in snow; (2) deficient wet pavement traction with the omission of a balance of circumferential grooves; and (3) good forward snow traction. Similarly, tread designs which are basically comprised of circumferential ribs have the following characteristics: (1) deficient forward snow traction; (2) good wet pavement traction with a balance of circumferential grooves; and (3) good lateral stability in snow. In addition, a tire tread design that has good wet or snow traction generally has poor dry traction, poor handling and often excessive noise levels. At the same time a tire tread which generally has good dry traction as well as handling and tread wear characteristically has poor wet and snow traction. Conflicting tire characteristics as these make it difficult to produce a tread pattern suitable for the various road conditions experienced by motorists during the several seasonal changes of an entire year.
The prior art has taken several design approaches relative to all-season tire tread designs, with one approach being that taught in U.S. Pat. No. 3,162,229 to Ellenrieder, et al. and U.S. Des. Pat. No. 223,599 to Busch, et al. which utilize asymmetric tread designs wherein the tire profile changes in the transverse direction but stays constant in a circumferential direction.
U.S. Pat. Nos. 3,004,578 to Braudorn and 3,861,436 to Poque disclose pluralities of adjoining tread sections which extend adjacent to one another in succession circumferentially of the tire wherein each of the adjacent sections differ from one another and impart to the tread various characteristics over their discreet circumferential extents. In another avenue of design, U.S. Pat. No. 2,534,869 to Jones utilizes two separate tread designs that are separated at the circumferential center plane of the tire, one side utilizing parallel ribs while the other side utilizes transverse bars. Similarly, U.S. Pat. No. 3,177,917 to Walters, et al. teaches the superimposition of circumferential and transverse elements to form a slipped plane concept of tread design to retain the desired functional characteristics and at the same time minimize the undesirable characteristics of both elements.
Another prior art all season tire is shown in FIG. 2 of published U.K. patent application No. 2,014,091A and basically utilizes a tread design having a central circumferentially extending rib together with a plurality of independent projections that are placed circumferentially about the tire so as to provide two circumferentially extending grooves, one on either side of the central rib, together with a plurality of lateral slots that extend transversely outwardly from the central grooves to the closest respective tread edge.
With all-season tire tread designs becoming more popular in the market place, it has been determined that the tread arrangement of the present invention which significantly differs from the prior art, is very suitable for use in all seasons and during all weather conditions and provides particularly good snow traction while still maintaining good wet and dry traction, low tread wear and noise levels as well as good handling.